U.K. Blocks Extradition of Alleged Hacker

LONDON—The U.K. blocked the extradition to the U.S. of a British computer hacker accused of accessing American military computers and proposed changes to its system of handing over suspected criminals, raising questions about extradition arrangements between the two long-standing allies.

British Home Secretary Theresa May on Tuesday said the U.K. wouldn't extradite Gary McKinnon to the U.S. on human-rights grounds, citing his battles...